No, the protection is for a 160m 90' high "T" with 8x 120' elevated
radials in a mostly treed area. That's a lot of exposure to induced or
trees to wires strikes. Since the elevated radials can't be grounded at
160m the protection problem is a bit different than buried radial
verticals. The trees average 110' and the vertical is about 100' from
the shack entrance panel, with buried RG8 and a remote tuner control line.
The T is fed with a 50:25 ohm TLT which does DC connect the vertical to
the radials but given lightning is an RF event that leaves some missing
protection, maybe blowing up the TLT.
The plan is to shunt any current to ground at the feedpoint from either
radials or vertical to a ground rod field and some TBD current path. A
high Z RF choke can provide a DC connection from the radials to ground,
but again there is inductance to consider.
The amp is solid state.
re GDT's, the spec on the axial leaded devices is 1.5pf.
Grant KZ1W
On 4/9/2017 0:07 AM, Roger (K8RI) on TT wrote:
I'm assuming this is for open wire feed line? That brings up the
question of the rig. Is it SS, or tube.
Is the tuner link coupled, or with a transformer? Is there a direct
path from the antenna "through" the tuner to the rig?
73, Roger (K8RI)
On 4/6/2017 5:35 PM, jimlux wrote:
On 4/6/17 12:29 PM, Grant Saviers wrote:
I've seen pictures of all sorts of gaps, two wires almost touching,
interlocking rings, adjacent spheres, Jacobs ladder like rods with
tapered spacing , etc. One amateur radio product uses automotive spark
plugs (non resistor) and is sold as a pair on a copper plate for open
wire feeders. However, a copper plumbing sweat fitting is soldered
over
the gap so it is impossible to measure the gap. My question is, if I
use a non resistor spark plug as a arc gap, is there any experience
that
can be shared about what the gap distance should be set to? I plan to
have a removable cover over the gap end for WX protection .
Are there better designs for a gap that are easy to fabricate and
weather/bug resistant?
breakdown of air is 70 kv/inch. That's in a uniform field at sea
level, and a sparkplug or wires or whatever will breakdown at a lower
level.
A typical auto gap of, say, 0.030" will break down at about 1.5-2kV.
No matter how small the gap, or how low the pressure, an air gap will
not breakdown at less than 327 volts (the minimum sparking voltage) -
you might get significant field emission or corona, but you won't get
a spark.
Argon has a much lower minimum sparking voltage - 137V
vacuum gaps have entirely different behavior, and it's a bit of an
arcane art to design a consistent breakdown voltage.
The commercial transient suppression gaps might have fairly high
parasitic C - they're basically a couple electrodes, a spacer, and a
fill gas like neon or argon- I'd spend the $3 and measure one at your
frequency of interest to see what the RF properties are.
But maybe it's a few pF, and you don't care?
And a second question: Gas discharge capsules are used in coax
lightning protection devices. A large variety of gas discharge
components are stocked at Mouse, Digikey, etc in various voltages and
Kamps. Is there any difference in the RF properties of the tube in the
in-line coax devices vs what I can buy a lot cheaper as a
component? eg
Littlefuse and TDK 800v @ 10Ka around $3ea.
http://www.littelfuse.com/~/media/electronics/datasheets/gas_discharge_tubes/littelfuse_gdt_cg_cg2_datasheet.pdf.pdf
Grant KZ1W
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